[clang] Reapply "[clang analysis][thread-safety] Handle return-by-reference..… (PR #68572)

[Aaron Puchert via cfe-commits]

https://github.com/aaronpuchert approved this pull request.

Assuming that this is otherwise identical to the Phab review. I would suggest to add some release notes (in a separate change).

https://github.com/llvm/llvm-project/pull/68572